In-flight refueling (or air-to-air refueling) is an important method for extending the range of both manned and unmanned aircraft traveling long distances over areas having no feasible landing or refueling points. Although in-flight refueling is a relatively common operation, especially for military aircraft, the passage of large amounts of fuel between a first aircraft (the tanker aircraft, for instance) and a second aircraft (the receiver aircraft, for instance) during an in-flight refueling operation may create a potentially dangerous situation, especially if components of the in-flight refueling system are allowed to move or oscillate in an uncontrolled manner. In addition, the close proximity of the first aircraft and the second aircraft during an in-flight refueling operation may create the danger of a mid-air collision between the aircraft. Such a danger may be increased if a component of an in-flight refueling system extending from the first aircraft is allowed to oscillate or move in an erratic manner relative to the first aircraft.
One conventional system for in-flight refueling is the probe and drogue in-flight refueling system wherein the first aircraft may extend an elongate flexible hose having an end attached to a drogue such that the second aircraft, having a refueling probe extending therefrom, may engage the drogue while in flight in order to initiate the transfer of fuel. An operator of the second aircraft is responsible for maneuvering the second aircraft such that the refueling probe extending therefrom may enter and engage the drogue. According to some conventional probe and drogue in-flight refueling systems, the engagement of the refueling probe with the drogue is accomplished as the second aircraft carefully accelerates with respect to the trailing drogue. The drogue may include, for instance, a catch mechanism for securing the refueling probe within the drogue so that the refueling probe may be securely fastened within the drogue during the transfer of fuel. The catch mechanism may also include a fuel valve that may be opened when the probe is secured within the drogue. Thus, fuel may be pumped from the first aircraft into the elongate hose and down to the fuel valve disposed in the drogue so as to pressurize the elongate hose prior to the engagement of the probe carried by the second aircraft.
The elongate hose extending from the first aircraft may trail directly aft and below a fuselage of the first aircraft, or, in some instances, it may trail directly aft and below a refueling pod that may be carried by the first aircraft on, for instance, a wing hardpoint. In both of these cases, the elongate hose may be exposed to high wind speeds as it is trailed behind the first aircraft. For instance, the first aircraft may travel at speeds between about 180 and 400 knots during a conventional in-flight refueling operation. During an in-flight refueling operation using a probe and drogue in-flight refueling system, the elongate hose may trail aft and below the first aircraft in a stable arc such that the drogue operably engaged with the end of the elongate hose may be held in a relatively stable position relative to the first aircraft. In such cases, an operator of the second aircraft may position the second aircraft such that a refueling probe extending therefrom may engage the relatively stable drogue.
As in all mechanical systems, however, the elongate hose and attached drogue may experience oscillatory vibrations in response to applied forces (such as for instance, wind forces, or the impact force encountered as the second aircraft engages the drogue). In some cases, the elongate hose (and attached drogue) may begin to oscillate uncontrollably (at for instance, a resonance frequency) with respect to the first aircraft such that the drogue may move in an erratic pattern with respect to the first aircraft such that it may become difficult for an operator of the second aircraft to maneuver the second aircraft such that the refueling probe extending therefrom may be engaged with the drogue. In such cases, the elongate hose, may, for instance, rise into an upward arc relative to the first aircraft and/or oscillate relative to the first aircraft. Such motion may not only make the in-flight refueling operation difficult but also endanger both the first and second aircraft if the motion becomes extreme. In addition, if the second aircraft engages the drogue at a relatively high closure rate, slack may be introduced in the elongate hose and a traveling wave (such as a sinusoid or “sine” wave) may be propagated in the elongate hose that may travel from the drogue to the tanker aircraft (or the in-flight refueling system pod carried thereby). The safety of the crews that may operate the first and second aircraft may be in danger if the elongate hose and attached drogue begin to impact the control surfaces, in-flight refueling system pod, or other structural components of the first or second aircraft.
In such cases, conventional probe and drogue in-flight refueling systems may provide a guillotine system for cutting and jettisoning the elongate hose should oscillations or movement of the elongate hose and attached drogue become erratic enough so as to endanger the operators and/or other crew of either the first or second aircraft. However, it is undesirable to jettison the elongate hose and attached drogue as the first aircraft must cease in-flight refueling operations and return to an airfield for costly and complex repairs to the in-flight refueling system. Also, it is especially undesirable to jettison the elongate hose while the second aircraft is engaged with the attached drogue, as a length of elongate hose may be left hanging from the refueling receptacle carried by the second aircraft and may damage the second aircraft by striking a control surface or by being taken into a jet intake of the second aircraft.
Conventional probe and drogue in-flight refueling systems may also provide an elongate hose retracting device (such as, for instance a drum roller) disposed, for instance, in the fuselage of the first aircraft or in an in-flight refueling system pod carried thereby, for retracting and stabilizing the hose with respect to the first aircraft. More particularly, the retracting device may act to take up excess slack in the elongate hose in order to shorten the extension of the elongate hose in an attempt to dampen the oscillation of the elongate hose. In some conventional systems, sensors may be provided in or near the hose take-up device either within a fuselage of the tanker aircraft or within an in-flight refueling system pod carried thereby). Such sensors are configured to detect slack in the elongate hose after it has been propagated up the length of the elongate hose to the location of the sensor. Such sensors have limited capacity to limit the damage that may be caused by traveling waves, however, as slack in the elongate hose may not be detected until the traveling wave has already reached the sensor, by which time, the elongate hose may have already struck and damaged the tanker aircraft or the in-flight refueling system pod carrying the sensor and take-up device.
Therefore, there exists a need for an in-flight refueling system, sensor system, and method for detecting slack and traveling oscillations in the elongate hose at the point where they begin (such as, for instance, near the drogue end of the elongate hose) such that the hose retracting device may be more quickly controlled to take-up the slack generated in the elongate hose so as to prevent potentially dangerous changes in disposition that may occur in probe and drogue in-flight refueling system components, such as for instance, an elongate hose trailing aft and below a first aircraft (serving as, for instance, a tanker aircraft). More particularly, there exists a need for a sensor system that may be more effective at detecting oscillations and/or changes in the disposition of the elongate hose that begin near the drogue end of the elongate hose and expeditiously transmitting signals to the retracting device such that such oscillations and/or changes in disposition may be effectively resisted by taking up a section of the elongate hose in response to the signals.
Thus, it would be advantageous to provide an in-flight refueling system, sensor system, and method for quickly detecting and damping oscillations or changes in the disposition of the elongate hose and attached drogue that may occur during an in-flight refueling operation. Also, it would be advantageous to provide a device for detecting and transmitting data related to oscillation of the elongate hose and attached drogue that is simple, robust, lightweight, and compact enough to be mounted on or near the drogue end of existing elongate hoses or on an existing drogue without the need to modify existing in-flight refueling system components.